Cyclic Voltammetry In Aqueous Solution Research Articles

Experimental and Virtual Screening of Phenazine and Phenothiazine Derivatives in Aqueous Solution for Electrochemical Carbon Capture

Molecular redox-active compounds, including quinone and aza-aromatics, have emerged as tools for capturing carbon dioxide using renewable electricity. Given the vast and highly diverse chemical space of the candidate compounds, accessing their electrochemical properties in a rapid way is attractive for both experimental and virtual screening approaches.Here we present a study on the experimental screening of a series of commercial redox-active compounds. Phenazine and phenothiazine dyes have been experimentally tested for applications in electrochemical carbon capture, for which they are finding increasing applications as redox mediators due to their unique redox properties in aqueous solution. Nicotinamide has been used as a redox-inactive solubilizing agent to increase the solubilities of general phenazine and phenothiazine derivatives for rapid experimental screening of commercial compounds without time-consuming synthetic modifications. Cyclic voltammetry in aqueous solutions under nitrogen and carbon dioxide indicated reversible behavior in the pH swing of an aqueous solution. Bulk electrolysis experiments demonstrated the chemical stability of phenazine and phenothiazine derivatives. The redox properties and the chemical stability make phenazine and phenothiazine derivatives interesting candidates for future use as redox-active materials in electrochemical carbon capture.We also present progress towards a virtual screening for the optimization of electrochemical and physicochemical properties of redox-active compounds. Based on our experimental screening of commercial phenazine and phenothiazine compounds identifying neutral red as the lead compound, a virtual screening was performed for optimization of electrochemical and physicochemical properties using machine learning. The virtual screening development steps include (1) chemical library generation using neutral red as a lead compound, (2) molecular property prediction based on quantum chemical calculations, (3) aqueous solubility prediction using machine learning, (4) data processing and database creation, and (5) experimental validation of the optimized compounds for the use of electrochemical carbon capture. Figure 1

The effect of CTAB, a cationic surfactant, on the adsorption ability of the boron-doped diamond electrode: Application for voltammetric sensing of Bisphenol A and Hydroquinone in water samples

The present study introduces for the first time the effect of the cationic surfactant, cetyltrimethylammonium bromide (CTAB) on the adsorption capability of the boron-doped diamond (BDD) electrode for the sensing of environmental pollutants bisphenol A (BPA) and hydroquinone (HQ). Cathodic pretreatment of the electrode surface after an anodic pretreatment exhibited a best electrochemical response for these two phenolic compounds. The electrochemical characteristics of BPA and HQ were first sufficiently documented by cyclic voltammetry in aqueous solutions without the addition of surfactant over a shorter and longer potential range. Square-wave voltammetry was employed for a detailed study depending on the operational conditions (e.g., pH and nature of supporting electrolyte, concentration of CTAB, accumulation variables, instrumental parameters, etc.). The sensitivity of the voltammetric measurements for BPA and HQ was increased when CTAB was present in strong acidic media (more effective for BPA) due to its interaction with the neutral forms of the selected compounds on the hydrophobic surface of BDD electrode. Besides, a significant increase in the detecting sensitivity of BPA in CTAB-containing solutions could be obtained after applying an accumulation process. Using square-wave stripping mode (after 30 s accumulation at open-circuit condition) in 0.1 M H2SO4 containing 1 × 10−4 M CTAB, the limits of detection were found to be 0.05 μg/mL (2.19 × 10-7 M), and 0.23 μg/mL (2.09 × 10-6 M) for the simultaneous determination of BPA and HQ, respectively. In this way, modification-free BDD electrode could introduce an alternative to chemically modified electrodes for the analysis of environmental samples.

Synthesis of quaternary nanocomposites for catalytic reduction of Cr(VI) to Cr(III) and its sensing

Alginate/Carboxymethylcellulose/Dex/MnO2/g-C3N4 (Alg/CMC/Dex/MnO2/g-C3N4) sol crosslinked with Ca2+ composite gel was synthesized by dissipative convective process followed by freeze drying process and characterized by Fourier transform infra red spectroscopy(FT-IR), Thermogravimetric analysis (TGA), Powder X-ray diffraction (PX-RD), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Brunauer-Emmett –Teller (BET) adsorption isotherm and Rheology. As synthesized composite was used electrochemical sensor for the detection of Cr(VI) by Cyclic Voltammetry in aqueous solutions over the range of 0.01 to 20.0 μg mL−1 with a detection limit of 0.63 ng mL−1 and 1.17 ng mL−1 respectively. The rheological behavior of the gel Alg/CMC/Dex/MnO2/g-C3N4/Ca showed elastic behavior dominating over viscous behavior with an increase of angular frequency sweep on account of showing gel like structures. The catalyst Alg/CMC/Dex/MnO2/g-C3N4/Ca reduced Cr(VI) to Cr(III) just in 1.20 min. in presence of 0.01 M NaBH4 which is due to its highest surface area among all as synthesized monoliths. The reduction of Cr (VI) became fast took only 26.63 s in presence of conc. H2SO4. The reaction kinetics became very fast when the catalyst amount is increased 0.006 g and the reaction cannot be measurable. The novelty of the catalyst Alg/CMC/Dex/MnO2/g-C3N4/Ca is that it does not need any acid or base to reduce Cr(VI) to Cr(III) in a minimum time reported.

Electrochemistry of Iron(II/III)‐N,N'‐ethylene‐bis‐(o‐hydroxyphenylglycine) Complexes in Aqueous Solution Indicates Potential for Use in Redox Flow Batteries

AbstractThe iron complexes of the two diastereomers of N,N′‐ethylene‐bis‐(o‐hydroxyphenylglycine) (EDDHA), racemic (R,R−S,S) and meso (R,S−S,R) were isolated from commercial Fe‐EDDHA fertilizer. Cyclic voltammetry in aqueous solution in the pH range between 4.0 and 11.5 indicated reversible behaviour at both mercury and glassy carbon electrodes and quasi reversible characteristics at a copper electrode. An E1/2 value of −642 mV (racemic diastereomer) and −615 mV (meso form) vs. Ag/AgCl 1 M NaCl reference electrode was observed at pH 9. In unbuffered solutions the complex of the racemic diastereomer shows almost pH independent redox behaviour over the whole pH range studied. The iron complex of the meso isomer hydrolyses at pH values above 9. Diffusion coefficients of the complex species were determined from the voltammograms for the meso isomer and the racemic form with 5.4 10−6 cm2 s−1 and 5.8 10−6 cm2 s−1 respectively. Bulk electrolysis experiments at pH 9 demonstrated the chemical stability of both the FeII‐ and the FeIII‐form of the complex with racemic EDDHA. Good cycling stability and current efficiency were obtained in subsequent charge/discharge experiments using a carbon felt electrode. The redox properties and the stability of FeII/III‐EDDHA complexes make them interesting candidates for future use as negative redox electrolytes in redox flow batteries (RFB).

Effect of Adsorption and Passivation Phenomena on the Electrochemical Oxidation of Phenol and 2-Chlorophenol at Carbon Black Diamond Composite Electrode

This work reports on the importance of adsorption and passivation phenomena during the electro-oxidation of phenolic mixture. A case study of the anodic oxidation of phenol and 2-chlorophenol was performed. A carbon black–diamond electrode with 20% carbon black (20CBD electrode) was used as the anode. The anodic oxidation behaviors of 100 mg/L phenol and 100 mg/L 2-chlorophenol on the 20CBD electrode were investigated using cyclic voltammetry in aqueous solutions of 0.25 M Na2SO4. The electrochemical impedance technique was used to investigate the effects of electrode passivation and the adsorption of phenol and 2-chlorophenol through the electrochemical degradation process. The results showed that oxidation of 2-chlorophenol was easier than that of phenol. Even in a 1:1 mixture of 2-chlorophenol and phenol, each at 100 mg/L, the removal rate of 2-chlorophenol was higher than that of phenol. After 6 h, up to 94% of the 2-chlorophenol had degraded, whereas only 20% of the phenol had degraded in the same ti...

Electron transfer in pH-sensitive nitroxide radicals

Two pH-sensitive stable nitroxide radicals are characterized by EPR spectroscopy and cyclic voltammetry in aqueous solution at different pH values. The rates of the photochemically-induced electron transfer reactions from the protonated and deprotonated forms of the radicals to a ruthenium complex are determined.

Evaluation of the electrochemical anion recognition of [formula omitted]-imprinted poly(Azure A) in [formula omitted] mixed solutions by ac-electrogravimetry

During the reversible electrochemical reactions of the intrinsically conducting polymer (ICP) films, ions are inserted in them to balance the inner charge site of the polymer. For this reason, doped ICP films with anions or cations can be good candidates for the electrochemical removal of contaminant ions from wastewater. In this work, a polymer of a phenothiazine derivative (poly(Azure A or PAA)) was electrosynthesized by cyclic voltammetry in aqueous solutions using nitrate ions as a structural template. After that, PAA film was repeatedly cycled in identical conditions in a monomer-free solution. The electrochemical anion recognition of the nitrate-imprinted poly(Azure A) (NO3−−PAA) was evaluated by the combination of electrochemical and mass impedance spectroscopy, the so called ac-electrogravimetry method. Ac-electrogravimetry allows the selectivity of NO3−−PAA to be quantified. NO3−−PAA exhibited a special sensitivity and selectivity for the nitrate ions over the interfering chloride ions in mixed NO3− and Cl− containing solutions. The Dixon plots of the kinetic constants obtained by ac-electrogravimetry were used as a graphical method to reveal that NO3− and Cl− transfers are non-competitive at lower doped states of the polymer but competitive at higher doped states. The reversibility of nitrate incorporation controlled by an external potential modulation, the relative low cost and easy synthesis render the NO3−−PAA film suitable in practical implications such as nitrate scavenger in aqueous contaminated environments.

Iron Phthalocyanine Electrodeposited Films: Characterization and Influence on Dopamine Oxidation

Electrodeposited films of iron phthalocyanine (FePc) were obtained by potential cycling and at fixed potential in 1,2-dichloroethane on glassy carbon and indium tin oxide electrodes and were characterized by cyclic voltammetry in aqueous solution. Films formed at constant potential were also characterized by electrochemical impedance spectroscopy. The mechanism of FePc film formation was investigated, with the FePc films being formed through interaction between the Pc macrocycle rings (π–π aggregates). The electrochemical oxidation of dopamine (DA) at the FePc modified electrodes in aqueous solution was probed. Raman spectroscopy showed a specific interaction between Fe atoms of the FePc complex and −NH2 groups in the dopamine molecules. The extensive interaction between the FePc film and DA in solution demonstrates the potential use of these modified electrodes for sensitive measurement of dopamine oxidation.

Electrochemistry Investigation of the Monolacunary and Their Transition Metal Substituent Keggin-Type Polyoxometalates

The electrochemical and electrocatalytic behaviors of [XW11O39] n− and [XW11M(H2O)O39] m− (X = B, Si, and P; MII = Mn, Co, and Ni) polyoxometalates were studied with specific emphasis on the tungsten centers by cyclic voltammetry in aqueous solution. Electrochemical studies show the two or three stepwise cathodic/anodic peaks corresponding to the redox processes of WVI centers. The reversibility of redox peaks increases for [SiW11M(H2O)O39]6− and [PW11M(H2O)O39]5− polyoxometalates; however, that of [BW11M(H2O)O39]7− maintains quasi-reversible. The redox waves of the W-O framework for all polyoxometalates are pH- and scan rate-dependent. The tungsten-centered waves for these compound show a classical potential shift as a function of acidity at pH = 2.2–4.2. The electrocatalysis behaviors of these compounds toward the reduction of nitrite ions have been studied in details. The plots of catalytic efficiency versus γ for [XW11O39] n− and [XW11M(H2O)O39] m− (X = B, Si, P; MII = Mn, Co, Ni) show the catalytic efficiency of [BW11O39]9− and [BW11M(H2O)O39]7− (M = Mn, Co, Ni) more than that of the other compounds which are mentioned in this article.

Anodic Degradation of 2-Chlorophenol by Carbon Black Diamond and Activated Carbon Composite Electrodes

A carbon black diamond composite electrode with 20% carbon black (20CBD) and activated carbon composite (ACC) electrode were prepared and used as anodes for 2-chlorophenol electro-oxidation. The electro-oxidation behaviors of 200mg/L 2-chlorophenol on 20CBD and ACC anodes were investigated by cyclic voltammetry in aqueous solutions of 0.5M H2SO4 (pH 0.55) and 0.25M Na2SO4 (pH 7). Results indicated that the 20CBD and ACC electrodes are more active at low pH than at high pH and that no oxidation peak appears on the ACC electrode. The performance of the 20CBD and ACC electrodes during degradation of 200mg/L 2-chlorophenol was investigated in an aqueous solution of pH 3 with 0.25M Na2SO4 as the supporting electrolyte and applied current density of 30mA/cm2. Results showed that the 20CBD electrode produced the best degradation rate, COD removal efficiency, and current efficiency. The degradation efficiencies of the 20CBD and ACC electrodes after 6h were 96% and 82.5%, respectively. The effects of solution pH, current density, and supporting electrolyte on the performance of the 20CBD were further investigated, and results showed that higher degradation rates are obtained at lower pH and with Na2SO4 as the supporting electrolyte. Removal efficiency also increased with increasing current density.

Silver nanoparticle decorated poly(2-aminodiphenylamine) modified carbon paste electrode as a simple and efficient electrocatalyst for oxidation of formaldehyde

This work describes the promising activity of silver nanoparticles on the surface of a poly(2-amino diphenylamine) modified carbon paste electrode (CPE) towards formaldehyde oxidation. Electrodeposition of the conducting polymer film on the CPE was carried out using consecutive cyclic voltammetry in an aqueous solution of 2-aminodiphenylamine and HCl. Nitrogen groups in the polymer backbone had a Ag ion accumulating effect, allowing Ag nanoparticles to be electrochemically deposited on the surface of the electrode. The electrochemical and morphological characteristics of the modified electrode were investigated. The electro-oxidation of formaldehyde on the surface of electrode was studied using cyclic voltammetry and chronoamperometry in aqueous solution of 0.1 mol/L NaOH. The electro-oxidation onset potential was found to be around −0.4 V, which is unique in the literature. The effect of different concentrations of formaldehyde on the electrocatalytic activity of the modified electrode was investigated. Finally, the diffusion coefficient of formaldehyde in alkaline media was calculated to be 0.47 × 10−6 cm2/s using chronoamperometry.

Electroanalytical Performance of a Freestanding Three‐Dimensional Graphene Foam Electrode

AbstractThe electroanalytical performance of a freestanding three‐dimensional (3D) quasi‐graphene macrostructure is evaluated and benchmarked towards model analytes in aqueous solutions. Due to the freestanding 3D graphene foam exhibiting near‐super‐hydrophobicity and consequently giving rise to poor voltammetric signatures in aqueous solutions (Brownson et al., J. Mater. Chem. A, 2013, 1, 5962), we explore a ‘washing’ pretreatment procedure to reduce the hydrophobic behaviour of the 3D graphene macrostructure in order to try and allow its effective application in such cases. Herein, the electrochemical properties and resultant electroanalytical performance of the pretreated 3D graphene foam (3D‐GF) is critically explored and compared to a freestanding 3D reticulated vitreous carbon (3D‐RVC) foam alternative towards the sensing of a range of important analytes via cyclic voltammetry in aqueous solutions; namely, uric acid (UA), acetaminophen (AP) and dopamine hydrochloride (DA). It is found that the 3D‐RVC exhibits improved electroanalytical characteristics with larger linear ranges and lower limit of detections achievable over that of the 3D‐GF towards the target analytes. This work provides a vital insight into electroanalysis using 3D graphene and carbon foams.

A novel electrochemical sensing platform for anions based on conducting polymer film modified electrodes integrated on paper-based chips

In this paper, conducting polymer film modified electrodes were applied to fabricate paper-based chips (PCs), and different concentrations of chloride ions (Cl−) in water can be selectively detected based on the potential response towards Cl−. The three-electrode system was screen-printed on paper and the polypyrrole (PPy) film doped with Cl− was electrochemically polymerized on working electrodes through cyclic voltammetry in aqueous solution. Open circuit potential-time method was used to measure the potential response. Based on such PCs, Cl− can be selectively detected in the range of 10−7–10−2M. Moreover, such PCs were utilized for Cl− analysis in real water samples and resulted in good results with recoveries between 113% and 124%. Besides, following the strategy we also employed this method to detect F− in water to demonstrate its general applicability. In view of its novelty, simplicity, sensitivity and low price, such PCs will potentially be utilized for the monitoring of anions in the environment, and our method made a start for the application of CMEs to PCs to design electrochemical sensors.

Hydrothermal Synthesis, Structural Determination, and Properties of a New Family of Mononuclear Lanthanide Complexes with Pyridines Bearing More Flexible Pendant-Arm Carboxylate Substituents

Members of a new family of mononuclear lanthanide complexes possessing the general formula Ln(3-pyrac)3(H2O)3 (Ln = Y 1, La 2, Sm 3, Eu 4, Gd 5, Tb 6, Dy 7, Er 8, 3-pyrac = 3-pyridylacetate) were synthesized by hydrothermal reaction and characterized by single-crystal x-ray diffraction analysis, infrared (IR) spectra, luminescent spectroscopy, and thermal analysis. Photoluminescence measurement indicates that the complexes 3, 4, 6, and 7 exhibit characteristic emission of Sm(III), Eu(III), Tb(III), and Dy(III) at room temperature. The electrochemical behavior of complexes 4 has been examined by cyclic voltammetry in aqueous solution.

Electrochemical Properties of Oxidized Carbon Nano‐Onions: DRIFTS‐FTIR and Raman Spectroscopic Analyses

The electrochemical reactions of carboxylic and lactone groups on carbon nano-onions (CNOs) in aqueous solutions result in non-Kolbe products: alcohols, ketones, ethers and epoxides. The anodic/cathodic conversion of ox-CNOs was assessed by Boehm titrations and by Raman and DRIFTS-FTIR (diffuse reflectance infrared Fourier transform spectroscopy). The electrochemical properties of oxidized carbon nano-onions were investigated by cyclic voltammetry in aqueous solutions. The ox-CNOs are electrochemically active as a result of the reduction of the oxygen-containing groups.

Synthesis, structure, and properties of a 1-D cerium based on monovacant Keggin-type polyoxotungstate

A new lanthanide-substituted polyoxometalate [(α-PW11O39)Ce(H2O)2]4− (1) has been synthesized in aqueous solution and characterized by elemental analysis, IR spectrum, UV spectroscopy, thermogravimetric analysis, X-ray powder diffraction (XRPD), and single-crystal X-ray diffraction. The structural analysis reveals that 1 consists of monovacant Keggin-type polyoxoanions [α-PW11O39]7− as the fundamental building blocks and four [(CH3)4 N]+ cations. Compound 1 exhibits a 1-D zigzag chain built by [(α-PW11O39)Ce(H2O)2]4− moieties. The electrochemical properties of 1 were investigated by cyclic voltammetry in aqueous solution with 0.5 mol L−1 Na2SO4 as the supporting electrolyte. Magnetic measurements reveal that 1 demonstrates spin–orbital coupling interactions and weak antiferromagnetic exchange interactions.

Controlled Electrochemical Formation of GexSbyTez using Atomic Layer Deposition (ALD)

This paper describes a systematic study of the deposition of a phase change material, GexSbyTez, using electrochemical atomic layer deposition (E-ALD). Cyclic voltammetry in aqueous solutions was used to investigate the deposition of atomic layers of Ge, Sb and Te. That data was used to develop initial E-ALD cycle conditions to form the binaries: SbxTey and GexTey. Films of the ternary material GexSbyTez, were then deposited with a wide range of compositions by alternating the binary cycles in various combinations. Conformal nanofilms were formed that exhibited good crystallinity.

Synthesis of silver nanowires and their applications in the electrochemical detection of halide

A silver nanowires modified platinum (Ag NWs/Pt) electrode was developed for simultaneous and selective determination of chloride, bromide and iodide ions by cyclic voltammetry in aqueous solutions. Silver nanowires were synthesized by an l-cysteine-assisted poly (vinyl pyrrolidone) (PVP)-mediated polyol route. X-ray diffraction (XRD) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were employed to investigate the prepared nanowires. The intrinsic high surface area and the fast electron transfer rate ascribed from the nanowire structure could further improve halide detection performance. The determination was based on measurement of the well-separated oxidation peak currents of respective silver halides formed on the surface of silver during an anodic potential sweep. The concentration range was linear from 50 μM to 20.2 mM for bromide and iodide and 200 μM to 20.2 mM for chloride, and the sensitivity was 0.059 μA/mM, 0.042 μA/mM and 0.032 μA/mM for chloride, bromide and iodide, respectively. The correlation coefficient was 0.999 in each case. The Ag NWs/Pt electrode offered a useful platform for the development of a highly sensitive halide sensor.

Assembly Chemistry between Lanthanide Cations and Monovacant Keggin Polyoxotungstates: Two Types of Lanthanide Substituted Phosphotungstates [{(α-PW11O39H)Ln(H2O)3}2]6− and [{(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO}2]10−

Two 2:2 types of monolanthanide substituted polyoxometalates [{(α-PW11O39H)Ln(H2O)3}2]6− (Ln = NdIII for 1 and GdIII for 2) and [{(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO}2]10− (Ln = SmIII for 3, EuIII for 4, GdIII for 5, TbIII for 6, HoIII for 7 and ErIII for 8) have been synthesized in aqueous solution and characterized by elemental analyses, IR spectra, UV−vis−NIR spectra, thermogravimatric analyses and single-crystal X-ray diffraction. The common structural features are that they are constructed from monovacant Keggin-type polyoxoanions [α-PW11O39]7− and trivalent lanthanide cations. Both 1 and 2 are essentially isomorphous, and the molecular structure is built by two symmetrically related monolanthanide substituted Keggin units [α-PW11O39Ln(H2O)3]4− linked via two Ln−O−W bridges, representing the first monovacant Keggin polyoxotungstate dimers constituted by two [α-PW11O39]7− polyoxoanions and two lanthanide cations in polyoxometalate chemistry. 3−8 are also isostructural and display another dimeric structure constructed from two monolanthanide substituted units [(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO]5− bridged by two (η2,μ-1,1)-acetato ligands. The photoluminescence properties of 4 and 6 were investigated at room temperature. Magnetic susceptibility measurements of 1, 3, 4, 7 and 8 between 2 and 300 K exhibit that their magnetic behaviors mainly result from the spin−orbital coupling interactions as well as weak antiferromagnetic exchange interactions within magnetic centers. The electrochemical properties of 1, 3, 4, 5, 7 and 8 were studied by means of cyclic voltammetry in aqueous solution with 0.5 M Na2SO4 as supporting electrolyte.

Electrochemical Growth of Iron Oxide Thin Films with Nanorods and Nanosheets for Capacitors

Porous iron oxide films with nanorods and nanosheets were anodically deposited onto the nickel substrates by a plating bath of , sodium acetate, and sodium sulfate at room temperature. Nucleation and growth mechanism of the iron oxide film was found to be an instantaneous nucleation and growth of two-dimensional cylindrical iron oxide. X-ray diffraction patterns show that the as-deposited iron oxide is orthorhombic , which converts into rhombohedral after annealing at temperature above . Annealing temperatures influences both the chemical composition and grain size of the film, and consequently determines the capacitive behavior of the film investigated by cyclic voltammetry in aqueous solution. An optimal annealing temperature of is obtained in terms of the film’s specific capacitance. Morphology of the film deposited at a current density higher than shows nanosheets, while the film deposited at a current density lower than shows nanorods. Specific capacitance of a film with nanosheets is higher than that of a film with nanorods.